Genes for resistance to and biodegradation of a number of organomercurials including the antiseptic merthiolate, the disinfectant phenylmercuric acetate, and the neuro-toxic fungicide, methyl mercury, are often found on bacterial plasmids along with resistance to simple inorganic mercury compounds, such as mercuric chloride. While the mechanism for resistance to inorganic mercury (mer) has been studied extensively at the biochemical and genetic levels, much less is known, particularly of the genetics and regulation of organomercury resistance. We propose to examine the organomercury resistance (Omr) locus of the plasmid, R831, by genetic and biochemical techniques. We will map the plasmid, includig the Omr fusions of the beta-galactosidase and lac permease genes to the promotors of the Omr locus using the Mud-1 "operon-fusion" bacteriophage. We will characterize both mutants and fusions for presence of the enzyme and transdport function(s) associated with the Omr locus and for their ability to synthesize mercury-inducible peptides in the mini-cell system. All mutants will be characterized by complementation analysis using previously defined mutants in the mer operons of R100 and Tn501. Initial genetic and physical mapping of the plasmid will provide information necessary for the cloning of functional units of the Omr locus. We are particularly interested in obtaining, for detailed study, the regulatory elements of the Omr locus including the promoter(s) and trans-acting regulatory proteins in order to compare them with analogous elements which we have isolated or are currently isolating from the mer operon of R100 and Tn501. We are also interested in obtaining the genes for the organomercurial lyase in order to do detailed biochemistry on this unusual enzyme. The cloned genes themselves will be useful for screening our large collection of multiply metal resistant bacterial for related sequences.